PC won't turn on unless CPU's power cable is unplugged.

[Witch]

I need help figuring out the problem and possibly a solution for my pc. It’s been shut off for a month or so but I recently used it a few days ago for about an hour before turning it off again till today. After the PC not turning on(fans don’t start, no lights turn on, etc) with me pressing the power button multiple times, I decided to open it up and see if I could find what component was causing the problem. Before I go over what I did, here’s a list of my components: (it is a pre-built so I’m not TOO familiar with the parts personally)

Motherboard: GA-H270M-D3H (rev. 1.0)
CPU: Intel Core i5-7400
GPU: GeForce GTX 1050 Ti
PSU: MasterWatt 600 Lite 80Plus White
RAM: 2x8gb no-brand ram sticks
SSD: WD Blue 500gb SATA

I’ve tried removing only the GPU and turning it on, didn’t work. I then tried starting it up with only 1 stick of RAM at a time on all 4 different slots but nothing either. I decided maybe I should take out and unplug all the components and wires before putting them back again so I did but it yielded no results. The PC finally showed some signs of life when I inexplicably tried turning it on without the CPU’s 12v 2x4 power cable plugged in, and the fans started and lights lit up! Lasting only for a few seconds before turning off quickly and turning itself on again. It kept repeating this process so I just assumed it couldn’t turn on without detecting power to the CPU. So I tried plug the 12v cables back but taking out only the CPU. From what I understood after some searching, the PC should’ve been able to “POST” without a CPU but give an error message afterwards and at that point I just wanted to see something on the monitor. Sadly it just went back to completely dead again with no fans or lights turning on.

In the end, no combination of CPU, GPU, or RAM lead to the PC even just turning on, and the only way I could find of making it show any signs of life was unplugging the 12v power cable for the CPU. Not sure how useful this information is but I did manage to measure 12v from the cable pins using my multimeter, so maybe this is an indication that the PSU isn’t the issue here? I’m not sure. Unfortunately I do not have any spare parts as this is was a pre-built PC and I’ve only recently started learning more about PC tech. I’d be happy to provide more information if it’s needed although I may need some clarifications here and there since I’m unfamiliar with certain terminologies.

[veeg]

Hello

Hopefully some of our members will chime in soon..

@Bruce

[phillpower2]

Highest failure rate first is the PSU then the MB, worse case scenario is the PSU goes out and takes the other hardware with it.

PSU: MasterWatt 600 Lite 80Plus White

Awful PSU so the first check would be to swap in a known good PSU for testing purposes, ask a friend or family member if you can borrow their PSU, anything 400W or above will do.

I did manage to measure 12v from the cable pins using my multimeter, so maybe this is an indication that the PSU isn’t the issue here?

As a PSU puts out various voltages +3.3V, +5V and +12V it may appear that the PSU is working correctly but it is not, any significant drop of any output can prevent the system from booting up, the other scenario is a significant increase in the output which can be worse as it can fry one or more major components such as the MB, CPU, RAM, add on video card etc.

Without a known good PSU you are going nowhere testing wise I`m afraid.

[Witch]

Without a known good PSU you are going nowhere testing wise I`m afraid.

Ah okay I see. Are there any good PSU brands you would recommend for my current setup and perhaps taking into account future CPU/GPU upgrades?

[phillpower2]

As per my reply #3;

first check would be to swap in a known good PSU for testing purposes, ask a friend or family member if you can borrow their PSU, anything 400W or above will do.

I would not purchase anything atm, if you cannot borrow an appropriate PSU the next best thing you can do is to get your PC checked by a local tech who will have spare parts that they can swap in for testing.

[phillpower2]

Abandoned thread closed.